1. Field of the Invention
In general, the systems and methods of this invention relate to time domain equalizer training. In particular, this invention relates to systems and methods for supplemental frequency domain training of the time domain equalizer in a discrete multi-tone system.
2. Description of Related Art
In Discrete Multi-tone Modulation (DMT) systems, the time domain equalizer (TDQ) is a finite impulse response (FIR) filter located at the receiver side of a DSL modem. The TDQ is used to reduce the intersymbol interference (ISI). If the channel is shortened in time to have a length no greater than the length of the cyclic prefix, the intersymbol interference can be eliminated. Thus, a common method for training the TDQ in a DMT system is to jointly optimize the numerator and denominator of the autoregressive (AR) model for the channel where the order of the numerator is equal to the cyclic prefix length and the denominator is used as the TDQ setting. The training is based on transmission and reception of a known reference signal, such as the reverb signal in ADSL systems, using a least squares fit of the AR channel model.